Due to advancements made in telecommunications and data transmission speeds (up to 100 MHz) over unshielded twisted pair cables, the connectors (jacks, patch panels, cross connects, etc.) have become a critical impediment to high performance data transmission at the higher frequencies, i.e., greater than 1 MHz. Some performance characteristics (particularly near end crosstalk) degrades beyond acceptable levels at these higher frequencies.
When an electrical signal is carried on a signal line which is in close proximity to another signal line or lines, such as in the case of adjacent pins or terminals in a connector, energy from one signal line can be coupled onto adjacent signal lines by means of the electric field generated by the potential between two signal lines and the magnetic field generated as a result of the changing electric field. This coupling, whether capacitive or inductive, is called crosstalk when this phenomenon occurs between two or more signal lines.
Crosstalk is a noise signal and degrades the signal-to-noise margin (S/N) of a system. In communications systems, reduced S/N margin results in greater error rates in the information conveyed on a signal line.
One way to overcome this crosstalk problem is to increase the spacing between the signal lines. Another method commonly used is to shield the individual signal lines. However in many cases, the wiring is pre-existing and standards define the geometries and pin definitions for connectors making the necessary changes to such systems cost prohibitive. In the specific case of communications systems using unshielded twisted pair wiring, certain standards defining connector geometries and pinout definitions were created prior to the need for high speed data communications.
These standards have created a large installed base of wiring and connectors and a need for connectors capable of meeting the requirements of today's high speed communications, while maintaining compatibility with the original connectors. The standard connector geometries and pinouts are such that a great deal of crosstalk occurs at these higher signal frequencies.
According to Fourier's theory, when a signal is added to an equal but opposite signal, the two signals cancel each other completely. In unshielded twisted pair wiring, the two wires which are twisted about each other carry identical but opposite signals. These signals are described as being differentially driven. As one signal is driven towards a more positive voltage level, the second signal is driven in the opposite direction or toward a more negative voltage level. These signals being equal but opposite generate fields that are equal but opposite. These equal and opposite fields cancel each other with the result that little crosstalk can occur between a twisted pair and other adjacent signal lines.
In a typical connector used in unshielded twisted pair wiring systems, the signals are conveyed through connector pins or terminals which are parallel to each other for an inch or more, allowing unacceptable levels of crosstalk to occur for today's high speed data signals. These signals are typically in line with each other with the fields from one signal line being coupled onto the one or two immediately adjacent lines. If a noise signal equal, but opposite to, the crosstalk coupled signal is induced onto the affected line, the two induced signals thus coupled will cancel each other. Since the connector carries complementary pairs of signals (i.e. two differentially driven signals of a twisted pair wiring), noise coupled from one line of one pair onto an adjacent line can be canceled by also coupling an equal amount of "noise" from its complement.